[feat] front: Vite/환경변수 타입 선언(vite-env.d.ts) 추가

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

front/src/vite-env.d.ts

@@ -0,0 +1,12 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  /** 현재 실행 환경 식별용 (local | dev | prod) */
+  readonly VITE_APP_ENV: 'local' | 'dev' | 'prod'
+  /** 백엔드 API 베이스 URL */
+  readonly VITE_API_BASE_URL: string
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv
+}